Low Temperature Method For Hermetically Joining Non-Diffusing Ceramic Materials In Multi-Layer Plate Devices

ABSTRACT

A method for the joining of ceramic pieces with a hermetically sealed joint comprising brazing a layer of joining material between the two pieces. The wetting and flow of the joining material is controlled by the selection of the joining material, the joining temperature, the joining atmosphere, and other factors. The ceramic pieces may be on a non-diffusable type, such as aluminum nitride, alumina, beryllium oxide, and zirconia, and the pieces may be brazed with an aluminum alloy under controlled atmosphere. The joint material is adapted to later withstand both the environments within a process chamber during substrate processing, and the oxygenated atmosphere which may be seen within the shaft of a heater or electrostatic chuck.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/489,014, which is a continuation of U.S. patent application Ser. No.14/292,804 to Elliot et al., filed May 30, 2014, now U.S. Pat. No.9,624,137, which is a continuation in part of U.S. patent applicationSer. No. 13/681,875 to Elliot et al., filed Nov. 20, 2012, now U.S. Pat.No. 8,789,743, which claims priority to U.S. Provisional Application No.61/565,396 filed Nov. 30, 2011 to Elliot et al., which is herebyincorporated by reference in its entirety, and which also claimspriority to U.S. Provisional Application No. 61/592,587 to Elliot etal., filed Jan. 30, 2012, which is hereby incorporated by reference inits entirety, and which also claims priority to U.S. ProvisionalApplication No. 61/605,707 to Elliot et al., filed Mar. 1, 2012, whichis hereby incorporated by reference in its entirety, and which alsoclaims priority to U.S. Provisional Application No. 61/658,896 to Elliotet al., filed Jun. 12, 2012, which is hereby incorporated by referencein its entirety, and which also claims priority to U.S. ProvisionalApplication No. 61/707,865 to Elliot et al., filed Sep. 28, 2012, whichis hereby incorporated by reference in its entirety, and which also is acontinuation in part of U.S. patent application Ser. No. 13/543,727 toElliot et al., filed Jul. 6, 2012, which is hereby incorporated byreference in its entirety.

BACKGROUND Field of the Invention

The present invention relates to methods for joining together objects,and more particularly to brazing methods for joining non-diffusingceramic objects.

Description of Related Art

The joining of ceramic materials may involve processes which requirevery high temperatures and very high contact pressures. For example,liquid phase sintering may be used to join ceramic materials together.In this type of manufacture, at least two drawbacks are seen. First, thehot pressing/sintering of a large, complex ceramic piece requires alarge physical space within a very specialized process oven. Second,should a portion of the finished piece become damaged, or fail due towear, there is no repair method available to disassemble the largepiece. The specialized fixturing, high temperatures, and inability todisassemble these assemblies invariably leads to very high manufacturingcosts.

Other processes may be geared towards strength, and may yield strongbonds between the pieces that, although structurally sufficient, do nothermetically seal the pieces. In some processes, diffusion bonding isused, which may take significant amounts of time, and may also alter theindividual pieces such that they form new compounds near the joint. Thismay render them unfit for certain applications, and unable to bereworked or repaired and rejoined.

Certain ceramics may allow for the joining of the ceramic pieces withhermetic joints at low temperatures. Ceramic materials may becategorized by their diffusability. The diffusability of the ceramic mayplay a part in whether low temperature brazing will result in hermeticjoining.

What is called for is a joining method for joining ceramic pieces at alow temperature and which provides a hermetic seal, and which allows forrepairs.

SUMMARY OF THE INVENTION

A method for the joining of ceramic pieces with a hermetically sealedjoint comprising brazing a layer of joining material between the twopieces. The wetting and flow of the joining material is controlled bythe selection of the joining material, the joining temperature, thejoining atmosphere, and other factors. The ceramic pieces may be of anon-diffusable type, such aluminum nitride, alumina, beryllium oxide,and zirconia, and the pieces may be brazed with an aluminum alloy undercontrolled atmosphere. The joint material is adapted to later withstandboth the environments within a process chamber during substrateprocessing, and the oxygenated atmosphere which may be seen within theshaft of a heater or electrostatic chuck.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a SEM cross-sectional view of a joint according to someembodiments of the present invention.

FIG. 2 is a SEM cross-sectional view of a joint according to someembodiments of the present invention.

FIG. 3 is a SEM cross-sectional view of a joint according to someembodiments of the present invention.

FIG. 4 is a SEM cross-sectional view of a joint according to someembodiments of the present invention.

FIG. 5 is a SEM cross-sectional view of a joint according to someembodiments of the present invention.

FIG. 6 is a sketch of an illustrative view of a joined ceramic assemblyaccording to some embodiments of the present invention.

FIG. 7 is a cross-sectional view of a joined ceramic assembly accordingto some embodiments of the present invention.

FIG. 8 is a perspective view of a ceramic piece with standoff mesasaccording to some embodiments of the present invention.

FIG. 9 is a cross-sectional view of a joint bridging differentatmospheres according to some embodiments of the present invention.

FIG. 10 is a view representing the joint integrity of a joint.

FIG. 11 is a view representing the joint integrity of a joint.

FIG. 12 is a view representing the joint integrity of a joint.

FIG. 13 is a view representing the joint integrity of a joint.

FIG. 14 is a view representing the joint integrity of a joint.

FIG. 15 is a view representing the joint integrity of a joint.

FIG. 16 is a view representing the joint integrity of a joint.

FIG. 17 is a view representing the joint integrity of a joint.

FIG. 18 is a view representing the joint integrity of a joint.

FIG. 19 is a view representing the joint integrity of a joint.

FIG. 20 is a view of a plate and shaft device used in semiconductorprocessing according to some embodiments of the present invention.

FIG. 21 is a sketch of a high temperature press and oven for a plateaccording to some embodiments of the present invention.

FIG. 22 is a sketch of a high temperature press and oven for a pluralityof plates according to some embodiments of the present invention.

FIG. 23 is a sketch of a high temperature press and oven for a plate andshaft device.

FIG. 24 is a cross-sectional view of a joint between a plate and shaftaccording to some embodiments of the present invention.

FIG. 25 is a cross-sectional view of a joint between a plate and shaftaccording to some embodiments of the present invention.

FIG. 26 is a perspective view of a shaft end with mesas according tosome embodiments of the present invention.

FIG. 27 is a partial cross-sectional view of a plate and shaft device inuse in semiconductor manufacturing according to some embodiments of thepresent invention.

FIG. 28 is a close-up cross-sectional view of a joint between and shaftand a plate according to some embodiments of the present invention.

FIG. 29 is view of a plate and shaft device according to someembodiments of the present invention.

FIG. 30 is an illustration of plate and shaft ready for assemblyaccording to some embodiments of the present invention.

FIG. 31 is an illustration of plate and shaft with fixturing ready forassembly according to some embodiments of the present invention.

FIG. 32 is an illustration of plate and shaft with fixturing ready forassembly according to some embodiments of the present invention.

FIG. 33 is an exploded view of a plate and shaft assembly with multipleconcentric joining layers according to some embodiments of the presentinvention.

FIG. 34 is a partial cross-sectional view of a heater with a multi-layerplate according to some embodiments of the present invention.

FIG. 35 is a partial cross-sectional view of a multi-layer plateaccording to some embodiments of the present invention.

FIG. 36 is a partial cross-sectional view of a multi-layer plateaccording to some embodiments of the present invention.

FIG. 37 is a partial cross-sectional view of a multi-layer plateaccording to some embodiments of the present invention.

FIG. 38 is a partial cross-sectional view of a multi-layer plateaccording to some embodiments of the present invention.

FIG. 39 is a partial cross-sectional view of a multi-layer plateaccording to some embodiments of the present invention.

FIG. 40 is a partial cross-sectional view of a multi-layer plateaccording to some embodiments of the present invention.

FIG. 41 is an illustration of an RF shield according to some embodimentsof the present invention.

FIG. 42 is a SEM cross-sectional view of a joint according to someembodiments of the present invention.

FIG. 43 is a SEM cross-sectional view of a joint according to someembodiments of the present invention.

FIG. 44 is a SEM cross-sectional view of a joint with a diffusingceramic.

FIG. 45 is a SEM cross-sectional view of a joint with a diffusingceramic.

FIG. 46 is a view representing the joint integrity of a joint.

FIG. 47 is a view representing the joint integrity of a joint.

FIG. 48 is a view representing the joint integrity of a joint.

FIG. 49 is a view representing the joint integrity of a joint.

FIG. 50 is a view representing the joint integrity of a joint.

FIG. 51 is a SEM cross-sectional view of a joint according to someembodiments of the present invention.

DETAILED DESCRIPTION

Some prior processes for the joining of ceramic materials requiredspecialized ovens, and compression presses within the ovens, in order tojoin the materials. For example, with liquid phase sintering, two piecesmay be joined together under very high temperatures and contactpressures. The high temperature liquid-phase sintering process may seetemperatures in the range of 1700 C and contact pressures in the rangeof 2500 psi.

Other prior processes may utilize diffusion of a joining layer into theceramic, and/or of the ceramic into the joining layer. In suchprocesses, a reaction at the joint area may cause changes to thematerial composition of the ceramic in the area near the joint. Thisreaction may depend upon oxygen in the atmosphere to promote thediffusion reaction.

In contrast to the aforementioned diffusion processes, joining methodsaccording to some embodiments of the present invention rely on controlof wetting and flow of the joining material relative to the ceramicpieces to be joined. In some embodiments, the absence of oxygen duringthe joining process allows for proper wetting without reactions whichchange the materials in the joint area. With proper wetting and flow ofthe joining material, a hermetically sealed joint can be attained atrelatively low temperature. In some embodiments of the presentinvention, a pre-metallization of the ceramic in the area of the jointis done prior to the joining process.

In some applications where end products of joined ceramics are used,strength of the joint may not be the key design factor. In someapplications, hermeticity of the joint may be required to allow forseparation of atmospheres on either side of the joint. Also, thecomposition of the joining material may be important such that it isresistant to chemicals which the ceramic assembly end product may beexposed to. The joining material may need to be resistant to thechemicals, which otherwise might cause degeneration of the joint, andloss of the hermetic seal. The joining material may also need to be of atype of material which does not negatively interfere with the processeslater supported by the finished ceramic device.

Ceramic end products manufactured according to embodiments of thepresent invention may be manufactured with considerable energy savingsrelative to past processes. For example, the lower temperatures used forjoining pieces with methods according the present invention, compared tothe high temperatures of prior liquid phase sintering processes used forjoining pieces, require less energy. In addition, there may beconsiderable savings in that the joining processes of the presentinvention do not require the specialized high temperature ovens, and thespecialized fixturing and presses required to generate the high physicalcontact stresses, required for prior liquid phase sintering processes.

An example of a joined ceramic end product which may be manufacturedaccording to embodiments of the present invention is the manufacture ofa heater assembly used in semiconductor processing.

FIG. 1 is a view of a cross-section of a joint 10 according to someembodiments of the present invention. The image is a as seen through aScanning Electron Microscope (SEM), and is taken at 20,000×magnification. A first ceramic piece 11 has been joined to a secondceramic piece 12 with a joining layer 13. In this exemplary embodiment,the first ceramic piece and second ceramic piece are made ofmono-crystalline aluminum nitride (AlN). The joining layer began asaluminum foil with 0.4 Wt. % Fe. The joining temperature was 1200 C andwas held for 120 minutes. The joining was done under a vacuum of7.3×10E−5 Torr, with a physical contact pressure across the joint ofapprox. 290 psi during joining.

FIG. 1 illustrates the joint with an upper boundary 15 between the firstceramic piece 11 and the joining layer 13, and a lower boundary 16between the joining layer 13 and the second ceramic piece 12. As seen atthe boundary regions at 20,000× magnification, no diffusion is seen ofthe joining layer into the ceramic pieces. No evidence of reactionwithin the ceramics is seen. The boundaries do not show any evidence ofvoids and do indicate that there was complete wetting of the boundariesby the aluminum during the joining process. The bright spots 14 seen inthe joining layer are an aluminum-iron compound, the iron being aresidue from the foil used for the joining layer.

FIG. 2 is a view of a cross-section of a joint 20 according to someembodiments of the present invention. The view is as seen through aScanning Electron Microscope (SEM), and is at 8,000× magnification. Afirst ceramic piece 21 has been joined to a second ceramic piece 22 witha joining layer 23. In this exemplary embodiment, the first ceramicpiece and second ceramic piece are made of mono-crystalline aluminumnitride (AlN). The joining layer began as aluminum foil with 0.4 Wt. %Fe. The joining temperature was 900 C and was held for 15 minutes. Thejoining was done under a vacuum of 1.9×10E−5 Torr, with a minimalphysical contact pressure across the joint during joining. The joininglayer 23 illustrates that after the joining of the first ceramic piece21 and the second piece 22 a residual layer of aluminum remains betweenthe joined pieces.

FIG. 2 illustrates the joint with an upper boundary 24 between the firstceramic piece 21 and the joining layer 23, and a lower boundary 25between the joining layer 23 and the second ceramic piece 22. As seen atthe boundary regions at 8,000× magnification, no diffusion is seen ofthe joining layer into the ceramic pieces. No evidence of reactionwithin the ceramics is seen. The boundaries do not show any evidence ofvoids and do indicate that there was complete wetting of the boundariesby the aluminum during the joining process. The bright spots 26 seen inthe joining layer contain Fe residue from the foil used for the joininglayer.

FIGS. 1 and 2 illustrate joints according to embodiments of the presentinvention in which ceramics, such as mono-crystalline aluminum nitride,are joined with a joining layer of aluminum that achieved full wettingduring the joining process. The joints show no evidence of diffusion ofthe joining layer into the ceramic, and no evidence of reaction areaswithin the joining layer or in the ceramic pieces. There is no evidenceof a chemical transformation within the ceramic pieces or the joininglayer. There is a residual layer of aluminum present after the joiningprocess.

FIG. 3 illustrates a joint 30 according to embodiments of the presentinvention using a polycrystalline aluminum nitride ceramic. In FIG. 3,the joining layer 32 is seen joined to the lower ceramic piece 31. Theview is as seen through a Scanning Electron Microscope (SEM), and is at4,000× magnification. In this exemplary embodiment, the first ceramicpiece is made of poly-crystalline aluminum nitride (AlN). The joininglayer began as aluminum foil with 0.4 Wt. % Fe. The joining temperaturewas 1200 C and was held for 60 minutes. The joining was done under avacuum of 2.4×10E−5 Torr, with a physical contact pressure across thejoint during joining of approximately 470 psi.

In some embodiments, the poly-crystalline AlN, such as the ceramic seenin FIGS. 3-5, is comprised of 96% AlN and 4% Yttria. Such a ceramic maybe used in industrial applications because during the liquid phasesintering used to manufacture the ceramic, a lower temperature may beused. The lower temperature process, in contrast to mono-crystallineAlN, reduces manufacturing energy consumption and costs of the ceramic.The poly-crystalline material may also have preferred properties, suchas being less brittle. Yttria and other dopants, such as Sm2O3, areoften used for manufacturability and tuning of material properties.

FIG. 3 illustrates the same lack of diffusion at the boundary 33 betweenthe joining layer 32 and the first ceramic piece 31, which is apoly-crystalline AlN ceramic, as was seen with the mono-crystallineexamples seen in FIGS. 1 and 2. Although the boundary 33 may appear tobe somewhat rougher than seen in FIGS. 1 and 2, this is a result of arougher original surface. No diffusion is seen along the boundary.

With a poly-crystalline AlN such as the 96% AlN-4% Yttria ceramic asseen in FIGS. 3-5, the ceramic presents grains of AlN which areinterspersed with yttrium aluminate. When this ceramic is presented withaluminum, such as joining layers according to some embodiments of thepresent invention, at higher temperature such as above the liquidustemperature of Al, the Al brazing material may react with the yttriumaluminate resulting in the dislodging and release of some of the AlNgrains at the surface of the ceramic.

FIG. 4 illustrates a joint 40 according to embodiments of the presentinvention using a polycrystalline aluminum nitride ceramic. In FIG. 4,the joining layer 43 is seen joining the upper ceramic piece 42 to thelower ceramic piece 41. The view is as seen through a Scanning ElectronMicroscope (SEM), and is at 8,000× magnification. In this exemplaryembodiment, the first ceramic piece is made of poly-crystalline aluminumnitride (AlN). The joining layer began as aluminum foil with 99.8% Al.The joining temperature was 1120 C and was held for 60 minutes. Thejoining was done under a vacuum of 2.0×10E−5 Torr, with a minimalphysical contact pressure across the joint during joining.

FIG. 4 illustrates some grains 46 of AlN within the joining layer 43.The grains 46 have migrated from the surface 44 of the upper ceramicpiece 42 and/or the surface 45 of the lower ceramic piece 41. The AlNgrains have been dislodged from the surface due to the aluminum of thejoining layer having attacked the yttrium aluminate between the grainsof the poly-crystalline AlN. The AlN grains themselves have not reactedwith the aluminum joining layer, nor is any sign of diffusion of thealuminum into the AlN grains seen. The non-susceptibility of AlN todiffusion with aluminum under the conditions of processes according toembodiments of the present invention had been previously seen in theexamples of mono-crystalline AlN of FIGS. 1 and 2, and is maintained inthe poly-crystalline example of FIG. 4.

FIG. 5 illustrates a joint 50 according to embodiments of the presentinvention using a poly-crystalline aluminum nitride ceramic. In FIG. 5,the joining layer 52 is seen joined to the upper ceramic piece 51. Theview is as seen through a Scanning Electron Microscope (SEM), and is at2,300× magnification. In this exemplary embodiment, the first ceramicpiece 51 is made of poly-crystalline aluminum nitride (AlN). The joininglayer began as aluminum powder with 5 Wt. % Zr. The joining temperaturewas 1060 C and was held for 15 minutes. The joining was done under avacuum of 4.0×10E−5 Torr, with a physical contact pressure across thejoint during joining of approximately 8 psi.

The joints as seen in the examples of FIGS. 1-5 may be used inapplications where a hermetically sealed joint between ceramic pieces isrequired. The prior process of hermetically joining ceramic pieces usingliquid phase sintering required very high temperatures, very specializedovens and presses, significant amounts of time, and were quite costly.The joining of ceramics with hermetically sealed joints using processesaccording to embodiments of the present invention require lowertemperatures, less extensive and less costly process ovens, less time,and result in significant cost savings. In addition, the joined piecesmay later be separated and reworked if desired. The joined pieces areseen with residual aluminum in the joint area between the joined ceramicpieces.

The joints seen in FIGS. 1-5 are aluminum nitride, and, as discussedabove, this ceramic is non-susceptible to diffusion during the joiningprocess. New research has shown that ceramics other than aluminumnitride also are able to be joined in this fashion with no measurablediffusion of aluminum into the ceramic. This category of ceramics hasbeen shown to be able to be joined to itself, or to other ceramicswithin the category, with hermetic joints using the methods describedherein. Among the non-diffusing ceramics in this category are aluminumnitride, alumina, zirconia, and beryllium oxide.

In contrast, other ceramics have been found to have significantdiffusion of aluminum into the ceramic. These ceramics have been foundto be joined with joints that are not hermetic joints using the methodsdescribed herein. Among the ceramics in this category are siliconcarbide and silicon nitride.

A new way of classifying ceramics has thus emerged in which a group ofceramics has been identified by its diffusability, and links thatdiffusability to the group's non-susceptability to diffusion by aluminumin the temperature ranges discussed herein. Together with the use oftemperatures in a range not typical of standard brazing temperatures,and using brazing materials as described herein, and with theatmospheres discussed herein, this group of ceramics may be joined withhermetic joints not formerly attainable. This group of ceramicscomprises aluminum nitride, alumina, zirconia, and beryllia. Otherceramics which are not susceptible to diffusion by aluminum would alsobe in this group.

FIGS. 42-45 are cross-sections of joints using ceramics which are notsusceptible to diffusion with aluminum, according to some embodiments ofthe present invention. The images are as seen through a ScanningElectron Microscope (SEM), and the scale is as shown in the lower rightof the images.

FIG. 42 illustrates a joint 500 according to embodiments of the presentinvention. In FIG. 42, the joining layer 501 is seen joining the upperceramic piece 502 to the lower ceramic piece 503. The view is as seenthrough a Scanning Electron Microscope (SEM), and is scaled as seen inthe display bar in the image. In this exemplary embodiment, the firstceramic piece and the second ceramic piece are made of beryllium oxide(BeO). The joining layer began as aluminum foil with 99.99% Al. Thejoining temperature was 800 C and was held for 10 minutes. The joiningwas done under a vacuum of 10E−6 Torr, with a minimal physical contactpressure across the joint during joining. The joining layer began as0.004 inch foil and the resulting joint was maintained at 0.0035 inchesthick using standoffs, as described below herein.

FIG. 42 illustrates that the BeO pieces have not reacted with thealuminum joining layer, nor is any sign of diffusion of the aluminuminto the BeO seen. The joint is seen with good and complete wetting ofthe aluminum to the BeO ceramic, and without voids. This joint washermetic. The non-susceptibility of BeO to diffusion with aluminum underthe conditions of processes according to embodiments of the presentinvention had been previously seen in the examples of AlN, and ismaintained with the use of BeO.

FIG. 43 illustrates a joint 505 according to embodiments of the presentinvention. In FIG. 43, the joining layer 506 is seen joining the upperceramic piece 507 to the lower ceramic piece 508. The view is as seenthrough a Scanning Electron Microscope (SEM), and is scaled as seen inthe display bar in the image. In this exemplary embodiment, the firstceramic piece is of alumina (Al₂O₃)) and the second ceramic piece aremade of yttria stabilized zirconia (YSZ). The joining layer began asaluminum foil with 99.99% Al. The joining temperature was 800 C and washeld for 10 minutes. The joining was done under a vacuum of 10E−6 Torr,with a minimal physical contact pressure across the joint duringjoining. The joining layer began as 0.004 inch foil and the resultingjoint was maintained at 0.0035 inches thick using standoffs, asdescribed below herein.

FIG. 43 illustrates that the alumina, and the zirconia pieces have notreacted with the aluminum joining layer, nor is any sign of diffusion ofthe aluminum into the Al₂O₃ or the YSZ seen. The joint is seen with goodand complete wetting of the aluminum to the ceramics, and without voids.This joint was hermetic. The non-susceptibility of Al₂O₃ or the YSZ todiffusion with aluminum under the conditions of processes according toembodiments of the present invention had been previously seen in theexamples of AlN and BeO, and is maintained with the use of Al₂O₃ and theYSZ. Energy dispersive x-ray analysis has verified that the aluminumjoint material has not diffused into the zirconia or the berylliumoxide, for example. In discussions herein the YSZ may be referred tosimply as zirconia.

In contrast, FIGS. 44 and 45 illustrate joints where the aluminumjoining layer has diffused into the ceramic. Also, the ceramic hasdiffused into the aluminum joining layer. Significantly, the joints werenot hermetic. FIG. 44 illustrates a joint 510 where the joining layer511 is seen joining the upper ceramic piece 512 to the lower ceramicpiece 513. The view is as seen through a Scanning Electron Microscope(SEM), and is scaled as seen in the display bar in the image. In thisexample, the first ceramic piece is of silicon nitride (SiN) and thesecond ceramic piece is also SiN. The joining layer began as aluminumfoil with 99.99% Al. The joining temperature was 800 C and was held for10 minutes. The joining was done under a vacuum of 10E−6 Torr, with aminimal physical contact pressure across the joint during joining. Thejoining layer began as 0.004 inch foil. The joint was not hermetic.

EDX analysis demonstrated that aluminum from the joint of FIG. 44diffused into SiN ceramic. Also, EDX analysis demonstrated that Si haddiffused into the aluminum brazing layer. The SiN was therefore not inthe group of non-diffusing ceramics which included the other ceramicsmentioned above.

FIG. 45 illustrates a joint 515 where the joining layer 516 is seenjoining the upper ceramic piece 517 to the lower ceramic piece 518. Theview is as seen through a Scanning Electron Microscope (SEM), and isscaled as seen in the display bar in the image. In this example, thefirst ceramic piece is of silicon carbide (SiC) and the second ceramicpiece is also SiC. The joining layer began as aluminum foil with 99.99%Al. The joining temperature was 800 C and was held for 10 minutes. Thejoining was done under a vacuum of 10E−6 Torr, with a minimal physicalcontact pressure across the joint during joining. The joining layerbegan as 0.004 inch foil. The joint was not hermetic.

EDX analysis demonstrated that aluminum from the joint of FIG. 45diffused into SiC ceramic. Also, EDX analysis demonstrated that Si haddiffused into the aluminum brazing layer. The SiC was therefore not inthe group of non-diffusing ceramics which included the other ceramicsmentioned above.

FIG. 6 illustrates an exemplary joined ceramic assembly 70. In someaspects, the joined ceramic assembly 70 is composed of a ceramic, suchas aluminum nitride. Other materials, such as alumina, zirconia, orberyllium oxide, may be used. In some aspects, a first ceramic piece 72may be aluminum nitride and a second ceramic piece 71 may be aluminumnitride, zirconia, alumina, or other ceramic. In some present processes,the joined ceramic assembly 70 components may first be manufacturedindividually in an initial process involving a process oven wherein thefirst piece 72 and the second piece 71 are formed.

FIG. 7 shows a cross section of an embodiment of a joint in which afirst ceramic piece 72 is joined to a second ceramic piece 71, which maybe made of the same or a different material, for example. A joiningmaterial, such as braze filler material 74, may be included, which canbe selected from the combinations of braze materials or bindersdescribed herein and may be delivered to the joint according to themethods described herein. With respect to the joint depicted in FIG. 7,the first ceramic piece 72 is positioned such that a joint interfacesurface 73A of the first ceramic piece 72 abuts the second ceramic piece71 along its joint interface surface 73,B with only the braze fillerinterposed between the surfaces to be joined. The thickness of the jointis exaggerated for clarity of illustration. In some embodiments, arecess may be included in one of the mating pieces, the first ceramicpiece 72 in this example, which allows the other mating piece to residewithin the recess.

An embodiment as illustrated in FIG. 7 may include a plurality ofstandoffs adapted to maintain a minimum braze layer thickness. In someembodiments, as seen in FIG. 8, one of the ceramic pieces, such as thesecond ceramic piece 71, may utilize a plurality of standoffs mesas 75on the end 73B of the second ceramic piece 71 which is to be joined tothe first ceramic piece 72. The mesas 75 may be part of the samestructure as the second ceramic piece 71, and may be formed by machiningaway structure from the piece, leaving the mesas. The mesas 75 may abutthe end 73A of the first ceramic piece 72 after the joining process. Insome embodiments, the mesas may be used to create a minimum braze layerthickness for the joint. In other embodiments, the minimum braze layerthickness for the joint is created by incorporating powdered materialinto the braze layer filler material. The largest particle size of thatincorporated powder material determines the minimum joint thickness. Thepowdered material may be mixed with powdered braze layer fillermaterial, or painted onto the ceramic joint surface, or painted onto thebraze layer filler foil of appropriate thickness, or incorporateddirectly into the braze layer filler material foil of appropriatethickness. In some embodiments, the braze layer material, prior tobrazing, will be thicker than the distance maintained by the mesas orpowder particles between the shaft end and the plate. In someembodiments, other methods may be used to establish a minimum brazelayer thickness. In some embodiments, ceramic spheres may be used toestablish a minimum braze layer thickness. In some aspects, the jointthickness may be slightly thicker than the dimension of the standoffs,or other minimum thickness determining device, as not quite all of thebraze material may be squeezed out from between the standoffs and theadjacent interface surface. In some aspects, some of the aluminum brazelayer may be found between the standoff and the adjacent interfacesurface. In some embodiments, the brazing material may be 0.006 inchesthick prior to brazing with a completed joint minimum thickness of 0.004inches. The brazing material may be aluminum with 0.4 Wt. % Fe. In someembodiments, the brazing material may be 0.004 inches thick prior tobrazing and with a completed joint thickness of 0.0035 inches. Brazelayers may be significantly thinner, and in some aspects the joininginterfaces may be smoothed or polished to allow for a very thinnerbrazing layer. FIG. 51 illustrates a 4 micron braze layer which resultedin a hermetic joint when brazing polished AlN pieces. The thin brazelayer is seen as a horizontal layer in the image. No diffusion isobserved.

As seen in FIG. 9, the brazing material may bridge between two distinctatmospheres, both of which may present significant problems for priorbrazing materials. On a first surface of the joint, the brazing materialmay need to be compatible with the processes occurring, and theenvironment 77 present, in the semiconductor processing chamber in whichthe joined ceramic assembly is to be used. On a second surface of thejoint, the brazing material may need to be compatible with a differentatmosphere 76, which may be an oxygenated atmosphere. Prior brazingmaterials used with ceramics have not been able to meet both of thesecriteria. For example, braze elements containing copper, silver, or goldmay interfere with the lattice structure of a silicon wafer beingprocessed in a chamber with the joined ceramic, and are thus notappropriate. However, in some cases, a surface of the brazed joint maysee a high temperature, and an oxygenated atmosphere. The portion of thebraze joint which would be exposed to this atmosphere will oxidize, andmay oxidize inwardly into the joint, resulting in a failure of thehermiticity of the joint. In addition to structural attachment, thejoint between joined ceramic pieces to be used in semiconductormanufacturing must be hermetic in many, if not most or all, uses.

A braze material which will be compatible with both of the types ofatmospheres described above when they are seen on both sides across ajoint in such a device is aluminum. Aluminum has a property of forming aself-limiting layer of oxidized aluminum. This layer is generallyhomogenous, and, once formed, prevents or significantly limitsadditional oxygen or other oxidizing chemistries (such a fluorinechemistries) penetrating to the base aluminum and continuing theoxidation process. In this way, there is an initial brief period ofoxidation or corrosion of the aluminum, which is then substantiallystopped or slowed by the oxide (or fluoride) layer which has been formedon the surface of the aluminum. The braze material may be in the form ofa sheet, a powder, a thin film, or be of any other form factor suitablefor the brazing processes described herein. For example, the brazinglayer may be a sheet having a thickness ranging from 0.00019 inches to0.011 inches or more. In some embodiments, the braze material may be asheet having a thickness of approximately 0.0012 inches. In someembodiments, the braze material may be a sheet having a thickness ofapproximately 0.006 inches. In some embodiments, the braze layer mayhave a thickness of 0.004 inches. Typically, alloying constituents (suchas magnesium, for example) in aluminum are formed as precipitates inbetween the grain boundaries of the aluminum. While they can reduce theoxidation resistance of the aluminum bonding layer, typically theseprecipitates do not form contiguous pathways through the aluminum, andthereby do not allow penetration of the oxidizing agents through thefull aluminum layer, and thus leaving intact the self-limitingoxide-layer characteristic of aluminum which provides its corrosionresistance. In the embodiments of using an aluminum alloy which containsconstituents which can form precipitates, process parameters, includingcooling protocols, would be adapted to minimize the precipitates in thegrain boundary. For example, in one embodiment, the braze material maybe aluminum having a purity of at least 99.5%. In some embodiments, acommercially available aluminum foil, which may have a purity of greaterthan 92%, may be used. In some embodiments, alloys are used. Thesealloys may include Al-5 w % Zr, Al-5 w % Ti, commercial alloys #7005,#5083, and #7075. These alloys may be used with a joining temperature of1100 C in some embodiments. These alloys may be used with a temperaturebetween 800 C and 1200 C in some embodiments. These alloys may be usedwith a lower or higher temperature in some embodiments.

The non-susceptibility of this group of ceramics to diffusion withaluminum under the conditions of processes according to embodiments ofthe present invention results in the preservation of the materialproperties, and the material identity, of the ceramic after the brazingstep in the manufacturing of the plate and shaft assembly.

In some embodiments, the joining process is performed in a processchamber adapted to provide very low pressures. Joining processesaccording to embodiments of the present invention may require an absenceof oxygen in order to achieve a hermetically sealed joint. In someembodiments, the process is performed at a pressure lower than 1×10E−4Torr. In some embodiments, the process is performed at a pressure lowerthan 1×10E−5 Torr. In some embodiments, further oxygen removal isachieved with the placement of zirconium or titanium in the processchamber. For example, a zirconium inner chamber may be placed around thepieces which are to be joined.

In some embodiments, atmospheres other than vacuum may be used toachieve a hermetic seal. In some embodiments, argon (Ar) atmosphere maybe used to achieve hermetic joints. In some embodiments, other noblegasses are used to achieve hermetic joints. In some embodiments,hydrogen (H2) atmosphere may be used to achieve hermetic joints.

The wetting and flow of the brazing layer may be sensitive to a varietyof factors. The factors of concern include the braze materialcomposition, the ceramic composition, the susceptibility of the ceramicto diffusion by aluminum, the chemical makeup of the atmosphere in theprocess chamber, especially the level of oxygen in the chamber duringthe joining process, the temperature, the time at temperature, thethickness of the braze material, the surface characteristics of thematerial to be joined, the geometry of the pieces to be joined, thephysical pressure applied across the joint during the joining process,and/or the joint gap maintained during the joining process.

In some embodiments, the surfaces of the ceramic may undergo ametallization prior to the placement of the ceramic pieces into achamber for joining. The metallization may be a frictional metallizationin some embodiments. The frictional metallization may comprise the useof an aluminum rod. A rotary tool may be used to spin the aluminum rodover areas which will be adjacent to the brazing layer when the piece isjoined. The frictional metallization step may leave some aluminum in thesurface of the ceramic piece. The frictional metallization step mayalter the ceramic surface somewhat, such as by removing some oxides,such that the surface is better adapted for wetting of the brazingmaterial.

An example of a brazing method for joining together first and secondceramic objects may include the steps of bringing the first and secondobjects together with a brazing layer selected from the group consistingof aluminum and an aluminum alloy disposed between the first and secondceramic objects, heating the brazing layer to a temperature of at least800 C, and cooling the brazing layer to a temperature below its meltingpoint so that the brazing layer hardens and creates a hermetic seal soas to join the first member to the second member. Another example of abrazing method for joining together first and second ceramic objects,wherein the ceramics are of a group consisting of aluminum nitride,alumina, beryllium oxide, and zirconia, may include the steps ofbringing the first and second objects together with a brazing layerselected from the group consisting of aluminum and an aluminum alloydisposed between the first and second ceramic objects, heating thebrazing layer to a temperature of at least 770 C, and cooling thebrazing layer to a temperature below its melting point so that thebrazing layer hardens and creates a hermetic seal so as to join thefirst member to the second member. Various geometries of braze jointsmay be implemented according to methods described herein.

A joining process according to some embodiments of the present inventionmay comprise some or all of the following steps. Two or more ceramicpieces are selected for joining. In some embodiments, a plurality ofpieces may be joined using a plurality of joining layers in the same setof process steps, but for the sake of clarity of discussion two ceramicpieces joined with a single joining layer will be discussed herein. Theceramic pieces may be of aluminum nitride. The ceramic pieces may be ofmono-crystalline or poly-crystalline aluminum nitride. The ceramicpieces may be selected from a group consisting of aluminum nitride,alumina, beryllium oxide, and zirconia, which is a group whichdemonstrates non-diffusability by aluminum. Other ceramics may be inthis group. Portions of each piece have been identified as the area ofeach piece which will be joined to the other. In an illustrativeexample, a portion of the bottom of a ceramic plate structure will bejoined to the top of a ceramic hollow cylindrical structure. The joiningmaterial may be a brazing layer comprising aluminum. In someembodiments, the brazing layer may be a commercially available aluminumfoil of >99% aluminum content. The brazing layer may consist of aplurality of layers of foil in some embodiments.

In some embodiments, the specific surface areas which will be joinedwill undergo a pre-metallization step. This pre-metallization step maybe achieved in a variety of ways. In one method, a frictionalpre-metallization process is employed, using a rod of material, whichmay be 6061 aluminum alloy, may be spun with a rotary tool and pressedagainst the ceramic in the joint area, such that some aluminum may bedeposited onto each of the two ceramic pieces in the area of the joint.In another method, PVD, CVD, electro-plating, plasma spray, or othermethods may be used to apply the pre-metallization.

Prior to joining, the two pieces may be fixtured relative to each otherto maintain some positional control while in the process chamber. Thefixturing may also aid in the application of an externally applied loadto create contact pressure between the two pieces, and across the joint,during the application of temperature. A weight may be placed on top ofthe fixture pieces such that contact pressure in applied across thejoint. The weight may be proportioned to the area of the brazing layer.In some embodiments, the contact pressure applied across the joint maybe in the range of approximately 2-500 psi onto the joint contact areas.In some embodiments the contact pressure may be in the range of 2-40psi. In some embodiments, minimal pressure may be used. The contactpressure used at this step is significantly lower than that seen in thejoining step using hot pressing/sintering as seen in prior processes,which may use pressures in the range of 2000-3000 psi.

In embodiments using mesas as standoffs, as seen in FIG. 8, the originalthickness of the brazing layer prior to the application of heat islarger than the height of the mesas. As the brazing layer temperaturereaches and exceeds the liquidus temperature, pressure across thebrazing layer between the pieces being joined will cause relative motionbetween the pieces until the mesas on a first piece contact an interfacesurface on a second piece. At that point, contact pressure across thejoint will no longer be supplied by the external force (except asresistance to repulsive forces within the brazing layer, if any). Themesas may prevent the brazing layer from being forced out of the jointarea prior to the full wetting of ceramic pieces, and may thus allowbetter and/or full wetting during the joining process. In someembodiments, mesas are not used.

The fixtured assembly may then be placed in a process oven. The oven maybe evacuated to a pressure of less than 5×10E−5 Torr. In some aspects,vacuum removes the residual oxygen. In some embodiments, a vacuum oflower than 1×10E−5 Torr is used. In some embodiments, the fixturedassembly is placed within a zirconium inner chamber which acts as anoxygen attractant, further reducing the residual oxygen which might havefound its way towards the joint during processing. In some embodiments,the process oven is purged and re-filled with pure, dehydrated purenoble gas, such as argon gas, to remove the oxygen. In some embodiments,the process oven is purged and re-filled with purified hydrogen toremove the oxygen.

The fixture assembly is then subjected to increases in temperature, anda hold at the joining temperature. Upon initiating the heating cycle,the temperature may be raised slowly, for example 15C per minute to 200C and then 20 C per minute thereafter, to standardized temperatures, forexample, 600 C and the joining temperature, and held at each temperaturefor a fixed dwell time to allow the vacuum to recover after heating, inorder to minimize gradients and/or for other reasons. When the brazetemperature has been reached, the temperature can be held for a time toeffect the braze reaction. In an exemplary embodiment, the dwelltemperature may be 800 C and the dwell time may be 2 hours. In anotherexemplary embodiment, the dwell temperature may be 1000 C and the dwelltime may be 15 minutes. In another exemplary embodiment, the dwelltemperature may be 1150 and the dwell time may be 30-45 minutes. In someembodiments, the dwell temperature does not exceed a maximum of 1200 C.In some embodiments, the dwell temperature does not exceed a maximum of1300 C. The dwell temperature may be in the range of 770 C and 1200 C insome embodiments. The dwell temperature may be in the range of 800 C and1200 C in some embodiments. Upon achieving sufficient braze dwell time,the furnace may be cooled at a rate of 20 C per minute, or lower whenthe inherent furnace cooling rate is less, to room temperature. Thefurnace may be brought to atmospheric pressure, opened and the brazedassembly may be removed for inspection, characterization and/orevaluation.

The use of too high of a temperature, for too long of a time period, maylead to voids forming in the joining layer as the result of significantaluminum evaporation. As voids form in the joining layer, thehermeticity of the joint may be lost. The process temperature and thetime duration of the process temperature may be controlled such that thealuminum layer does not evaporate away, and so that a hermetic joint isachieved. The use of too low of a temperature has been found to resultin a joint which is not hermetic. Standard brazing techniques use abraze temperature at or slightly above the melting point of the brazematerial. A temperature other than that standard brazing temperature isneeded when joining according to aspects of the present invention. Withproper temperature and process time duration control, in addition to theother process parameters described above, a continuous joint may beformed. A continuous joint achieved in accord with embodiments asdescribed herein will result in a hermetic sealing of the parts, as wellas a structural attachment.

The brazing material will flow and allow for wetting of the surfaces ofthe ceramic materials being joined. When a non-diffusing ceramic such asaluminum nitride, alumina, beryllium oxide, or zirconia is joined usingaluminum brazing layers and in the presence of sufficiently low levelsof oxygen and described herein, the joint is a hermetic brazed joint.This stands in contrast to the diffusion bonding seen in some priorceramic joining processes.

In some embodiments, the pieces to be joined may be configured such thatno pressure is placed across the brazing layer during brazing. Forexample, a post or shaft may be placed into a countersunk hole or recessin a mating piece. The countersink may be larger than the exteriordimension of the post or shaft. This may create an area around the postor shaft which then may be filled with aluminum, or an aluminum alloy.In this scenario, pressure placed between the two pieces in order tohold them during joining may not result in any pressure across the brazelayer. Also, it may be possible to hold each piece in the preferred endposition using fixturing such that little or no pressure is placedbetween the pieces at all.

Joined assemblies joined as described above result in pieces withhermetic sealing between the joined pieces. Such assemblies are thenable to be used where atmosphere isolation is an important aspect in theuse of the assemblies. Further, the portion of the joint which may beexposed to various atmospheres when the joined assemblies are later usedin semi-conductor processing, for example, will not degrade in suchatmospheres, nor will it contaminate the later semi-conductorprocessing.

Both hermetic and non-hermetic joints may join pieces strongly, in thatsignificant force is needed to separate the pieces. However, the factthat a joint is strong is not determinative of whether the jointprovides a hermetic seal. The ability to obtain hermetic joints may berelated to the wetting of the joint. Wetting describes the ability ortendency of a liquid to spread over the surface of another material. Ifthere is insufficient wetting in a brazed joint, there will be areaswhere there is no bonding. If there is enough non-wetted area, then gasmay pass through the joint, causing a leak. Wetting may be affected bythe pressure across the joint at different stages in the melting of thebrazing material. The use of mesa standoffs, or other standoff devicesuch as the insertion of ceramic spheres or powder particles ofappropriate diameter, to limit the compression of the brazing layerbeyond a certain minimum distance may enhance the wetting of the areasof the joint. Careful control of the atmosphere seen by the brazingelement during the joining process may enhance the wetting of the areasof the joint. In combination, careful control of the joint thickness,and careful control of the atmosphere used during the process, mayresult in a complete wetting of the joint interface area that is notable to be achieved with other processes. Further, the use of a brazinglayer that is of a proper thickness, which is thicker than the mesastandoff height, in conjunction with the other referenced factors, mayresult in a very well wetted, hermetic, joint. Although a variety ofjoining layer thicknesses may be successful, an increased thickness ofthe joining layer may enhance the success rate of the joint's hermeticaspect.

Acoustic imaging of the joint allows for viewing of the uniformity ofthe joint, and for determination of whether voids and/or passages existin the joint. The resulting images of joints tested to be hermetic showuniform, voidless joints, while images of joints tested to benon-hermetic show voids, or large non-bonded areas, in the ceramic-brazelayer interface area. In the examples seen in the acoustic images, ringshave been bonded to a flat surface. The rings are typically 1.40 inchesouter diameter, 1.183 inches interior diameter, with a joint interfacearea of approximately 0.44 square inches. The bonding of rings to a flatsurface are exemplary of the joining of a hollow shaft to a plate, asmay be seen in the assembly of a heater, for example.

FIG. 10 is an image created using acoustic sensing of the jointintegrity of a joint created according to the present invention. Thejoint was between two pieces of poly-crystalline aluminum nitride. Thebrazing layer material was three layers each of 0.0006″ thickness of99.8% aluminum foil in concert with a frictional metallization stepusing 6061 Aluminum alloy. The joining temperature was 1100 C held for45 minutes. The joining was done within a zirconium box in a processchamber held at pressure lower than 1×10E−5 Torr. No standoffs wereused. The image displays a solid dark color in locations where there isgood wetting onto the ceramic. The white/light areas are indicative of avoid at the joining surface of the ceramic. As seen, there is good andsufficient integrity of the joint. This joint was hermetic. Hermeticitywas verified by having a vacuum leak rate of <1×10E−9 sccm He/sec; asverified by a standard commercially available mass spectrometer heliumleak detector.

FIG. 11 is an image created using acoustic sensing of the jointintegrity of a joint created according to the present invention. Thejoint was between two pieces of poly-crystalline aluminum nitride. Thebrazing material was two layers of 99.8% aluminum foil with a frictionalmetallization step using 6061 Aluminum alloy. The joining temperaturewas 1100 C held for 45 minutes. The joining was done within a zirconiumbox in a process chamber held at pressure lower than 1×10E−5 Torr. Theimage displays a solid dark color in locations where there is goodwetting onto the ceramic. The white/light areas are indicative of a voidat the joining surface of the ceramic. As seen, there is good andsufficient integrity of the joint. This joint was hermetic.

FIG. 12 is an image created using acoustic sensing of the jointintegrity of a joint. The joint was between two pieces ofpoly-crystalline aluminum nitride. The brazing material was three layersof 99.8% aluminum foil without a frictional metallization step. Thejoining temperature was 1100 C held for 45 minutes. The joining was donewithin a zirconium box in a process chamber held at pressure lower than1×10E−5 Torr. The image displays a solid dark color in locations wherethere is good wetting onto the ceramic. The white/light areas areindicative of a void at the joining surface of the ceramic. As seen,there is integrity of the joint. This joint was hermetic. However, itcan be seen that some areas of voids come close together from each side.The joint maintained hermetic integrity but more voids were apparentthan in the cases with frictional metallization described above.

FIG. 13 is an image created using acoustic sensing of the jointintegrity of a joint. The joint was between two pieces ofpoly-crystalline aluminum nitride. In this joint, mesa standoffs wereused to maintain a minimum joint thickness. Three mesas were on thecircular shaft element. The mesas were 0.004 inches high. The brazingmaterial was aluminum of >99%. The brazing layer was 0.006 inches thickprior to brazing. The joining temperature was 1200 C held for 30minutes. The joining was done in a process chamber held at pressurelower than 1×10E−5 Torr. An applied load of 18 pounds was used to applypressure across the joint. The standoffs prevented the joint thicknessfrom becoming lower than the standoff height. In this case of using aset of standoff mesas, the wetting of the joint is seen to be superiorto that seen in the prior joint images. There is full wetting of thejoint and an absence of voids. This joint was hermetic. The use of thestandoff mesas to create a minimum joint thickness, in conjunction withthe high vacuum, results in a joint that is of the very high qualitythat is demonstrated by the acoustic image. The location of the threestandoff mesas is indicated by the three dots seen within the joint,spread equally radially.

FIG. 14 is an image created using acoustic sensing of the jointintegrity of a joint. The joint was between two pieces ofpoly-crystalline aluminum nitride. The brazing material was two layersof 99.8% aluminum foil without a frictional metallization step. Therewere no standoffs determining the minimum joint thickness. The joiningtemperature was 1100 C held for 45 minutes. The joining was done withina zirconium box in a process chamber held at pressure lower than 1×10E−5Torr. The image displays a solid dark color in locations where there isgood wetting onto the ceramic. The white/light areas are indicative of avoid at the joining surface of the ceramic. This joint was not hermetic.The brazing layer was thinner than in the example of FIG. 12. Asdescribed above, the thickness of the brazing material is one of thefactors which determines whether a joining process will result reliablyin a hermetically sealed joint.

FIG. 15 is an image created using acoustic sensing of the jointintegrity of a joint. The joint was between two pieces ofpoly-crystalline aluminum nitride. The brazing material was three layersof 7075 aluminum alloy foil without a frictional metallization step. Thejoining temperature was 1100 C held for 45 minutes. The joining was donewithout using a zirconium box, in a process chamber held at pressurelower than 1×10E−5 Torr. The image displays a solid dark color inlocations where there is good wetting onto the ceramic. The white/lightareas are indicative of a void at the joining surface of the ceramic.This joint was hermetic, although a multiplicity of voids is seen. Asdescribed above, the amount of oxygen available to the joint undertemperature is one of the factors which determines whether a joiningprocess will result in a hermetically sealed joint. FIGS. 14 and 15 areexamples of how a process using multiple thin layers for brazing, andwithout standoff mesas, even in high vacuum, may result in non-uniformwetting. Although the joint is hermetic, the lack of wetting and thesignificant amount of voids indicate that this process approach may notbe as reliable as the use of a single piece brazing element. Incontrast, FIG. 13 illustrates the complete wetting seen with the use ofstandoff mesas, a single piece brazing element, and a high vacuumatmosphere.

FIG. 16 is an image created using acoustic sensing of the jointintegrity of a joint. The joint was between two pieces ofpoly-crystalline aluminum nitride. In this joint, mesa standoffs wereused to maintain a minimum joint thickness. Three mesas were on thecircular shaft element. The mesas were 0.004 inches high. The brazingmaterial was aluminum of >99%. The brazing layer was 0.006 inches thickprior to brazing. The joining temperature was 1150 C held for 30minutes. The joining was done in a process chamber held at atmosphericpressure in an argon gas environment. The supplied argon was 99.999%purity, and was passed through a dehumidifier prior to entering theprocess chamber. A flow rate of several slm (standard liters per minute)was used during the braze process. The standoffs prevented the jointthickness from becoming thinner than the standoff height. In this caseof using a set of standoff mesas, the wetting of the joint is seen to bevery uniform and complete. The location of the three standoff mesas isindicated by the three dots seen within the joint, spread equallyradially. There is full wetting of the joint and a near absence ofvoids. This joint was hermetic. The use of the standoff mesas to createa minimum joint thickness, in conjunction with the high purity argon,results in a joint that is of the very high quality that is demonstratedby the acoustic image.

FIG. 17 is an image created using acoustic sensing of the jointintegrity of a joint. The joint was between two pieces ofpoly-crystalline aluminum nitride. In this joint, mesa standoffs wereused to maintain a minimum joint thickness. Three mesas were on thecircular shaft element. The mesas were 0.004 inches high. The brazingmaterial was aluminum of >99%. The brazing layer was 0.006 inches thickprior to brazing. The joining temperature was 1150 C held for 30minutes. The joining was done in a process chamber held at atmosphericpressure in a hydrogen gas environment. The supplied hydrogen gas was99.999% purity, and further was passed through a purifier prior toentering the process chamber. A flow rate of several slm was used duringthe braze process. The standoffs prevented the joint thickness frombecoming lower than the standoff height. The location of the threestandoff mesas is indicated by the three dots seen within the joint,spread equally radially. In this case of using a set of standoff mesas,the wetting of the joint is seen to be very uniform and complete. Thereis full wetting of the joint and a near absence of voids. This joint washermetic. The use of the standoff mesas to create a minimum jointthickness, in conjunction with the high purity hydrogen gas, results ina joint that is of the very high quality that is demonstrated by theacoustic image.

FIG. 18 is an image created using acoustic sensing of the jointintegrity of a joint. The joint was between two pieces ofpoly-crystalline aluminum nitride. In this joint, mesa standoffs wereused to maintain a minimum joint thickness. Three mesas were on thecircular shaft element. The mesas were 0.004 inches high. The brazingmaterial was aluminum of >99%. The brazing layer was 0.006 inches thickprior to brazing. The joining temperature was 1150 C held for 30minutes. The joining was done in a process chamber held at atmosphericpressure in a nitrogen gas environment. The supplied nitrogen gas was99.999% purity. A flow rate of several slm was used during the brazeprocess. The standoffs prevented the joint thickness from becoming lowerthan the standoff height. In this case, the wetting of the joint is seento be not uniform and not complete. There is not full wetting of thejoint, and there are observable voids. This joint was not hermetic. Theuse of high purity nitrogen gas results in a joint that is not of thevery high quality that is demonstrated by the acoustic images of thevacuum, argon, and hydrogen gasses.

FIG. 19 is an image created using acoustic sensing of the jointintegrity of a joint. The joint was between two pieces ofpoly-crystalline aluminum nitride. In this joint, mesa standoffs wereused to maintain a minimum joint thickness. Three mesas were on thecircular shaft element. The mesas were 0.004 inches high. The brazingmaterial was aluminum of >99%. The brazing layer was 0.006 inches thickprior to brazing. The joining temperature was 1100 C held for 30minutes. The joining was done in a process chamber held at atmosphericpressure in a regular air atmosphere environment. The standoffsprevented the joint thickness from becoming lower than the standoffheight. In this case, the wetting of the joint is seen to be not uniformand not complete. There is not full wetting of the joint, and there areobservable voids. This joint was not hermetic. The use of regularatmosphere results in a joint that is not of the very high quality thatis demonstrated by the acoustic images of the vacuum, argon, andhydrogen gasses.

FIGS. 18 (nitrogen) and 19 (air) illustrate that the use of standoffmesas alone may not result in a high quality, fully wetted, voidless,and hermetic joint. FIG. 13 (high vacuum) illustrates that the use ofstandoff mesas and high vacuum results in a high quality, fully wetted,voidless, and hermetic joint. This relatively low temperature joiningprocess using aluminum as the brazing layer, and using processparameters according to embodiments of the present invention, results ina high quality hermetic joining of components, especially ceramiccomponents. Processes according to embodiments of the present inventionallow for low cost high quality joining of ceramic components, and alsoallow for disjoining of the components at a later time, if desired.FIGS. 16 (argon) and 17 (hydrogen) illustrate that non-vacuum processescan result in a high quality hermetic joint if the atmosphere iscarefully and properly controlled. In such embodiments, non-oxidizinggasses such as hydrogen, or high purity noble gasses, are used todisplace oxygen and nitrogen in the chamber.

The presence of a significant amount of oxygen or nitrogen during thebrazing process may create reactions which interfere with full wettingof the joint interface area, which in turn may result in a joint that isnot hermetic. Without full wetting, non-wetted areas are introduced intothe final joint, in the joint interface area. When sufficient contiguousnon-wetted areas are introduced, the hermeticity of the joint is lost.

The presence of nitrogen may lead to the nitrogen reacting with themolten aluminum to form aluminum nitride, and this reaction formationmay interfere with the wetting of the joint interface area. Similarly,the presence of oxygen may lead to the oxygen reacting with the moltenaluminum to form aluminum oxide, and this reaction formation mayinterfere with the wetting of the joint interface area. Using a vacuumatmosphere of pressure lower than 5×10−5 Torr has been shown to haveremoved enough oxygen and nitrogen to allow for fully robust wetting ofthe joint interface area, and hermetic joints. In some embodiments, useof higher pressures, including atmospheric pressure, but usingnon-oxidizing gasses such as hydrogen or pure noble gasses such asargon, for example, in the process chamber during the brazing step hasalso led to robust wetting of the joint interface area, and hermeticjoints. In order to avoid the oxygen reaction referred to above, theamount of oxygen in the process chamber during the brazing process mustbe low enough such that the full wetting of the joint interface area isnot adversely affected. In order to avoid the nitrogen reaction referredto above, the amount of nitrogen present in the process chamber duringthe brazing process must be low enough such that the full wetting ofjoint interface area is not adversely affected.

The selection of the proper atmosphere during the brazing process,coupled with maintaining a minimum joint thickness, may allow for thefull wetting of the joint. Conversely, the selection of an improperatmosphere may lead to poor wetting, voids, and lead to a non-hermeticjoint. The appropriate combination of controlled atmosphere andcontrolled joint thickness along with proper material selection andtemperature during brazing allows for the joining of materials withhermetic joints.

The temperature needed to result in a properly wetted and hermetic jointis a temperature higher than a standard brazing temperature. Thefollowing data illustrates the temperature zone wherein the jointtransforms from a non-hermetic to a hermetic joint when usingnon-diffusing ceramics, and in accord with other aspects as describedherein.

Temperature - ° C. Hermeticity 675 Leaks 675 Leaks 675 Leaks 675 Leaks750 Leaks 750 Leaks 750 Leaks 750 Leaks 760 Leaks 770 Hermetic 780Hermetic 790 Hermetic 800 Hermetic 800 Hermetic 900 Hermetic

The table above illustrates that there is a transition temperature abovewhich a hermetic joint may be achieved when non-diffusing ceramics arejoined according to the other aspects of the present invention. Whenrounded to the nearest 50 C increment, the minimum temperature requiredwould be 800 C. When rounded to the nearest 10 C increment, the minimumtemperature required would be 770 C.

Diffusion, of aluminum into a ceramic, for example, is a thermallyactivated process driven by concentration differences and obeys Fick'sLaws. Diffusivity is given by:

D=Do*exp(−Q _(d) /k _(B) *T)

-   -   Where    -   D=diffusivity    -   D₀=temperature independent constant    -   Q_(d)=Activation energy for diffusion    -   k_(B)=Boltzmann's constant    -   T=temperature

The activation energy may be the most important quantity here. Forceramic compounds with a quite large Q, diffusion may be unlikely in thecompound.

FIGS. 46-50 illustrate the joint integrity of joints formed at differenttemperatures near the transition temperature wherein the joint becomes afully wetted hermetic seal. These figures illustrate the temperaturesensitivity of the process such that a temperature significantly higherthan the melting point of the brazing material must be used in order toachieve a hermetic joint. The joints seen in FIGS. 46-50 all underwentthe same process with the exception of temperature. For each joint, thejoint joined an AlN ring to an AlN plate. Each joint began with an Albrazing layer of 99.99% Al foil beginning at 0.004 inches thick, with acompleted joint thickness of 0.0035 inches. The atmosphere was vacuum at10E−6 Torr, and the temperature was held for 10 minutes. The joint ofFIG. 46 was joined at 750 C and was not hermetic. Wetting was notcomplete and voids are seen. The joint of FIG. 47 was joined at 760 Cand was not hermetic. Wetting was not complete and voids are seen. Thejoint of FIG. 48 was joined at 770 C and the wetting is substantiallycomplete. The joint was hermetic. The joint of FIG. 49 was joined at 780C and the wetting is complete, and the joint was hermetic. The joint ofFIG. 50 was joined at 790 C and the wetting is complete, and the jointwas hermetic.

Based upon the data referred to herein, a temperature of greater than770 C may be used to join according to embodiments of the presentinvention. Temperatures in the range of 770 C to 1200 C may be used tojoin according to embodiments of the present invention.

Another advantage of the joining method as described herein is thatjoints made according to some embodiments of the present invention mayallow for the disassembly of components, if desired, to repair orreplace one of those two components. Because the joining process did notmodify the ceramic pieces by diffusion of a joining layer into theceramic, the ceramic pieces are thus able to be re-used.

Prior methods of manufacturing components such as heaters andelectrostatic chucks using ceramic materials have required process stepswith specialized atmospheres (such as vacuum, inert, or reducingatmospheres), very high temperatures, and very high contact pressures.The contact pressures may be applied using presses, and these pressesmay be adapted to operate inside a process chamber that provides thespecialized atmospheres, such as vacuum, and high temperatures. This mayrequire specialized presses and fixturing made of refractory materials,such as graphite, within the process chamber. The cost and complexity ofthese setups may be very high. In addition, the larger the componentthat is required to be pressed, the fewer components can be put intosuch a process oven. As the duration of the processes in the processovens with presses may be measured in days, and given the large expenseassociated with both the manufacture of and the running of the processovens/presses, a reduction in the number of steps which use theseprocess ovens which provide very high temperature, special atmospheres,and very high contact pressures during the manufacture of componentswill result in great savings.

FIG. 20 illustrates an exemplary plate and shaft device 100, such as aheater, used in semiconductor processing. In some aspects, the plate andshaft device 100 is composed of a ceramic, such as aluminum nitride. Theheater has a shaft 101 which in turn supports a plate 102. The plate 102has a top surface 103. The shaft 101 may be a hollow cylinder. The plate102 may be a flat disc. Other subcomponents may be present. In somepresent processes, the plate 102 may be manufactured individually in aninitial process involving a process oven wherein the ceramic plate isformed.

FIG. 21 conceptually illustrates a process oven 120 with a press 121.The plate 122 may be compressed under temperature in a fixture 123adapted to be pressed by the press 121. The shaft 101 may also besimilarly manufactured in a process step. In a typical process, theplate and shaft are formed by loading of aluminum nitride powderincorporating a sintering aide such as yttria at about 4 weight % into amold, followed by compaction of the aluminum nitride powder into a“solid” state typically referred to as “green” ceramic, followed by ahigh-temperature liquid-phase sintering process which densifies thealuminum nitride powder into a solid ceramic body. The high temperatureliquid-phase sintering process may see temperatures in the range of 1700C and contact pressures in the range of 2500 psi. The bodies are thenshaped into the required geometry by standard grinding techniques usingdiamond abrasives.

There are multiple functions of the shaft: one is to providevacuum-tight electrical communication through the wall of the vacuumchamber in order to apply electrical power to heater elements as well asa variety of other electrode types which may be embedded within theheater plate. Another is to allow temperature monitoring of the heaterplate using a monitoring device such as a thermocouple, and allowingthat thermocouple to reside outside of the processing chamber in orderto avoid interaction such as corrosion between the materials of thethermocouple and the process chemicals, as well as allowing thethermocouple junction to operate in a non-vacuum environment for rapidresponse. Another function is to provide isolation of the materials usedfor the previously mentioned electrical communication from theprocessing environment. Materials used for electrical communication aretypically metallic, which could thereby interact with process chemicalsused in the processing environment in ways which could be detrimental tothe processing results, and detrimental to the lifetime of the metallicmaterials used for electrical communication.

Given the relatively flat nature of the plate, a plurality of plates 142may be formed in a single process by stacking a plurality of platemolding fixtures 143 along the axial direction of the press 141 whichresides within the process oven 140, as seen conceptually in FIG. 22.The shafts may also be formed in a similar process using the press inthe process oven.

In the overall process of manufacturing a heater used in semiconductorprocessing both the step of forming plates and forming shafts requiresignificant commitments of time and energy. Given the cost of thespecialized high temperature ovens, and that the process steps offorming the plates and forming the shafts each may require the use of aspecialized process oven for days, a considerable investment of bothtime and money has been invested just to get the overall process to thepoint where the shaft and plate have been completed. Yet a further stepin the specialized process oven is required in present processes toaffix the plate to the shaft. An example of this step would be to jointhe shaft to the plate using a liquid phase sintering step in thespecialized high temperature process oven with a press. This third stepin the specialized process oven also requires significant space in sucha process oven as the assembled configuration of the heater includesboth the length of the shaft and the diameter of the plate. Although themanufacture of just the shafts may take a similar amount of axiallength, the diameter of the shafts is such that multiple shafts may beproduced in parallel in a single process.

As seen in FIG. 23, the joining process to sinter the shaft to the plateagain requires the use of a process oven 160 with a press 161. A set offixturing 164, 165 is used to position the plate 162 and the shaft 163,and to transmit the pressure delivered by the press 161.

Once the heater is completed, it may be used in semiconductorprocessing. The heater is likely to be used in harsh conditions,including corrosive gasses, high temperatures, thermal cycling, and gasplasmas. In addition, the heater may be subject to inadvertent impacts.Should the plate or the shaft become damaged, the opportunities forrepair of a plate and shaft device joined by liquid phase sintering arelimited, perhaps non-existent.

Another prior method for joining ceramic shafts to ceramic platesinvolves the bolting of the shaft to the plate. Such systems are nothermetic even where the adjoining surfaces are polished to enhance thequality of the seal. A constant positive purge gas pressure is requiredinto the inside of the shaft to reduce process gas infiltration.

An improved method for manufacturing semiconductor processing equipmentmay involve the joining of a shaft and a plate, which have beendescribed above, into a final joined assembly without the time consumingand expensive step of an additional liquid phase sintering with hightemperatures and high contact pressures. The shaft and plate may bejoined with a brazing method for joining ceramics.

FIG. 24 shows a cross section of an embodiment of a joint in which afirst ceramic object, which may be a ceramic shaft 181, for example, maybe joined to a second ceramic object, which may be made of the same or adifferent material, and which may be a ceramic plate 182, for example. Abraze filler material 180 may be included, which can be selected fromthe combinations of braze materials or binders described herein and maybe delivered to the joint according to the methods described herein.With respect to the joint depicted in FIG. 24, the shaft 181 ispositioned such that it abuts the plate, with only the braze fillerinterposed between the surfaces to be joined, for example end surface183 of the end 185 of the shaft 181 and an interface surface 184 of theplate 182. The thickness of the joint is exaggerated for clarity ofillustration.

FIG. 25 shows a cross section of a second embodiment of a joint in whicha first ceramic object, which may be a ceramic shaft 191, for example,may be joined to a second ceramic object, which may be made of the sameor a different material, and which may be a ceramic plate 192, forexample. A joining material, such as brazing layer 190, may be included,which can be selected from the combinations of braze layer materialsdescribed herein and may be delivered to the joint according to themethods described herein. In some aspects, the plate may be aluminumnitride, or another non-diffusing ceramic, and the shaft may bezirconia, alumina, or another non-diffusing ceramic. In some aspects, itmay be desired to use a shaft material with a lower conductive thermaltransfer coefficient in some embodiments. In some aspects, it may bedesired to use a zirconia shaft with an aluminum nitride plate.

With respect to the joint depicted in FIG. 25, the shaft 191 ispositioned such that it abuts the plate, with only the brazing layerinterposed between the surfaces to be joined, for example surface 193 ofthe shaft and surface 194 of the plate. The interface surface 194 of theplate 192 may reside in a recess 195 in the plate. The thickness of thejoint is exaggerated for clarity of illustration.

The embodiments as illustrated in FIGS. 24 and 25 may include aplurality of standoffs adapted to maintain a controlled minimum brazelayer thickness. In some embodiments, as seen in FIG. 26, the shaft 191may utilize a plurality of mesas 171 on the end 172 of the shaft 191which is to be joined to the plate. The mesas 171 may be part of thesame structure as the shaft 191, and may be formed by machining awaystructure from the shaft, leaving the mesas. In some embodiments, themesas may be used to create a controlled minimum braze layer thicknessof the remainder of the shaft end 172 from the mating surface of theplate. In some embodiments, the braze filler material, prior to brazing,will be thicker than the distance maintained by the mesas between theshaft end and the plate. With appropriate tolerance control on theinterface surface of the plate and of the shaft and mesas, the tolerancecontrol of the finished plate and shaft device may be achieved as themesas move to contact the plate interface during the brazing step. Insome embodiments, other methods may be used to establish a minimum brazelayer thickness. In some embodiments, ceramic spheres may be used toestablish a minimum braze layer thickness.

As seen in FIG. 27, the brazing material may bridge between two distinctatmospheres, both of which may present significant problems for priorbrazing materials. On an external surface 207 of the semiconductorprocessing equipment, such as a heater 205, the brazing material must becompatible with the processes occurring in, and the environment 201present in, the semiconductor processing chamber 200 in which the heater205 will be used. The heater 205 may have a substrate 206 affixed to atop surface of the plate 203, which is supported by a shaft 204. On aninternal surface 208 of the heater 205, the brazing layer material mustbe compatible with a different atmosphere 202, which may be anoxygenated atmosphere. Prior brazing materials used with ceramics havenot been able to meet both of these criteria. For example, brazeelements containing copper, silver, or gold may interfere with thelattice structure of the silicon wafer being processed, and are thus notappropriate. However, in the case of a brazed joint joining a heaterplate to a heater shaft, the interior of the shaft typically sees a hightemperature, and has an oxygenated atmosphere within the center of a thehollow shaft. The portion of the braze joint which would be exposed tothis atmosphere will oxidize, and may oxidize into the joint, resultingin a failure of the hermeticity of the joint. In addition to structuralattachment, the joint between the shaft and the plate of these devicesto be used in semiconductor manufacturing must be hermetic in many, ifnot most or all, uses.

In an exemplary embodiment, the plate and shaft may both be of aluminumnitride and both have been separately formed previously using a liquidphase sintering process. The plate may be approximately 9-13 inches indiameter and 0.5 to 0.75 inches thick in some embodiments. The shaft maybe a hollow cylinder which is 5-10 inches long with a wall thickness of0.1 inches. The plate may have a recess adapted to receive an outersurface of a first end of the shaft. As seen in FIG. 26, mesas may bepresent on the end of the shaft which abuts the plate. The mesas may be0.004 inches high. The plate and shaft may be fixtured together for ajoining step with a brazing material of aluminum foil placed between thepieces along the end of the shaft and within the recess of the plate.The brazing material may be 0.006 inches thick prior to brazing with acompleted joint minimum thickness of 0.004 inches. The brazing materialmay be aluminum with 0.4 Wt. % Fe. In some embodiments, the brazingmaterial may be 0.004 inches thick prior to brazing with a completedjoint minimum thickness of 0.0035 inches.

FIG. 28 illustrates a joint 220 used to join a plate 215 to a shaft 214according to some embodiments of the present invention. The joint 220has created a structural and hermetic joint which structurally supportsthe attachment of the plate 215 to the shaft 214. The joint 220 hascreated a hermetic seal which isolates the shaft atmosphere 212 seen bythe interior surface 218 of the shaft 214 from the chamber atmosphere211 seen along the exterior surface 217 of the shaft 214 and within theprocess chamber. The joint 220 may be exposed to both the shaftatmosphere and the chamber atmosphere and must therefore be ablewithstand such exposure without degradation which may result in the lossof the hermetic seal. In this embodiment, the joint may be aluminum andthe plate and the shaft may be ceramic such as aluminum nitride. In someembodiments, the joint 220 may be of aluminum, and which substantiallyremains in the joint region after the joining process. The residualaluminum may allow for disjoining of the joint for repair, rework, orother reasons.

FIG. 29 shows one embodiment of a schematic illustration of a heatercolumn used in a semiconductor processing chamber. The heater 300, whichmay be a ceramic heater, can include a radio frequency antenna 310, aheater element 320, a shaft 330, a plate 340, and a mounting flange 350.One embodiment of a brazing method for joining together a shaft 330 anda plate 340, both or either one of which may be made of aluminumnitride, to form the heater 300 may be implemented as follows.

A sheet of aluminum or aluminum alloy may be provided between the shaftand the plate, and the shaft and the plate may be brought together withthe sheet of the brazing layer disposed therebetween. The brazing layermay then be heated in a vacuum to a temperature of at least 800 C andcooled to a temperature below 600 C so that the brazing layer hardensand creates a hermetic seal joining the shaft to the plate. The shaft ofsaid heater may be of solid material or it may be hollow inconformation. In some aspects, the brazing temperature is at least 770C. In some aspects, the brazing temperature is in the range of 770 C to1200 C.

The fixturing may put a contact pressure of approximately 2-200 psi ontothe joint contact area. In some embodiments the contact pressure may bein the range of 2-40 psi. The contact pressure used at this step issignificantly lower than that seen in the joining step using hotpressing/sintering as seen in prior processes, which may use pressuresin the range of 2000-3000 psi. With the much lower contact pressures ofthe present methods, the specialized presses of the previous methods arenot needed. The pressures needed for the joining of the plate to theshaft using the present methods may be able to be provided using simplefixturing, which may include a mass placed onto the fixturing usinggravity to provide the contact pressure. In some embodiments, contactbetween the interface portion of the shaft and the brazing element, aswell as contact between the interface portion of the plate and thebrazing element, will provide contact pressure sufficient for joining.Thus, the fixture assembly need not be acted upon by a press separatefrom the fixture assembly itself. The fixtured assembly may then beplaced in a process oven. The oven may be evacuated to a pressure of1×10E−5 Torr. In some aspects, vacuum is applied to remove residualoxygen. In some embodiments, a vacuum of lower than 1×10E−4 Torr isused. In some embodiments, a vacuum of lower than 1×10E−5 Torr is used.Of note with regard to this step is that the high temperature oven withhigh contact pressure fixturing, which was required during themanufacture of the ceramic components (shaft and plate), is not neededfor this joining of the shaft and plate. When a minimum joint thicknessis maintained, such as with the use of standoffs, the contact pressureacross the joint need only be sufficient to allow the standoffs to meetthe interface area of the adjacent ceramic. There may be a very thinlayer of braze material between the standoff and the adjacent interfacearea, as the liquid braze material may not be fully cleared between thestandoff and the adjacent interface area.

In some embodiments, the plate and shaft may comprise differentceramics. The plate may be adapted to provide a high conductive heatcoefficient, whereas the shaft may be adapted to provide a lowerconductive heat coefficient such that heat is not lost down the shafttowards the mounting appurtenances of the process chamber. For example,the plate may be made of aluminum nitride and the shaft may be made ofzirconia.

FIGS. 30-32 illustrate a joining process which may join a shaft to aplate according to some embodiments of the present invention. Thejoining process may be run in a process oven with lower temperatures,contact pressures, and lower time and cost commitments than in previousjoining operations.

In some embodiments, as seen in FIG. 30, alignment and location of theshaft and plate is maintained by part geometries, eliminating fixturingand post-bond machining. Weighting may be used to insure there is nomovement during bonding process, other than some axial movement as thebraze material melts. The plate 400 may be placed top down with ajoining element 402 within a recess 403 in the back surface of the plate400. The shaft 401 may be inserted vertically downward into the recess403 within the plate 400. A weight 404 may be placed on the shaft 401 toprovide some contact pressure during the joining process.

In some embodiments, as seen in FIG. 31, location of the shaft and plateis maintained by part geometries, reducing post-bond machining.Fixturing may be required to maintain perpendicularity between shaft andplate during bond processing. In some embodiments, the tolerance controlof the mesas and the interface portion of the plate may be used tocontrol the dimensions and tolerances of the final assembly. Weightingmay also be used to insure there is no movement during bonding process,other than some axial movement as the braze material melts. The plate410 may be placed top down with a joining element 412 within a recess413 in the back surface of the plate 410. The shaft 411 may be insertedvertically downward into the recess 413 within the plate 410. A fixture415 is adapted to support and locate the shaft 411. A weight 414 may beplaced on the shaft 411 to provide some contact pressure during thejoining process. In some embodiments, a weight is not used. In someembodiments, the mass of the items to be joined may provide force, withgravity, to apply pressure between the items to be joined.

In some embodiments, as seen in FIG. 32, location and perpendicularityof shaft/plate is maintained by fixturing. Fixturing may not be precisedue to thermal expansion and machining tolerances—therefore, post-bondmachining may be required. The shaft diameter may be increased toaccommodate required material removal to meet final dimensionalrequirements. Again, weighting may be used to insure there is nomovement during bonding process, other than some axial movement as thebraze material melts. The plate 420 may be placed top down with ajoining element 422 above the back surface of the plate 420. The shaft421 may be placed onto the plate 420 to create a plate and shaftpre-assembly. A fixture 425 is adapted to support and locate the shaft421. The fixture 425 may be keyed to the plate to provide positionalintegrity. A weight 424 may be placed on the shaft 411 to provide somecontact pressure during the joining process.

Upon initiating the heating cycle, the temperature may be raised slowly,for example 15C per minute to 200 C and then 20 C per minute thereafter,to standardized temperatures, for example, 600 C and the joiningtemperature, and held at each temperature for a fixed dwell time toallow the vacuum to recover after heating, in order to minimizegradients and/or for other reasons. When the braze temperature has beenreached, the temperature can be held for a time to effect the brazereaction. In an exemplary embodiment, the dwell temperature may be 800 Cand the dwell time may be 2 hours. In another exemplary embodiment, thedwell temperature may be 1000 C and the dwell time may be 15 minutes. Inanother exemplary embodiment, the dwell temperature may be 1150 and thedwell time may be 30-45 minutes. In some embodiments, the dwelltemperature does not exceed a maximum of 1200 C. In some embodiments,the dwell temperature does not exceed a maximum of 1300 C. Uponachieving sufficient braze dwell time, the furnace may be cooled at arate of 20 C per minute, or lower when the inherent furnace cooling rateis less, to room temperature. The furnace may be brought to atmosphericpressure, opened and the brazed assembly may be removed for inspection,characterization and/or evaluation.

An aspect of the current invention is the maximum operating temperatureof the bonded shaft-plate as defined by the decreasing tensile strength,with temperature, of the aluminum or aluminum alloy selected for thejoining. For example, if pure aluminum is employed as the joiningmaterial, the structural strength of the bond between the shaft andplate becomes quite low as the temperature of the joint approaches themelting temperature of the aluminum, generally considered to be 660 C.In practice, when using 99.5% or purer aluminum, the shaft-plateassembly will withstand all normal and expected stresses encountered ina typical wafer processing tool to a temperature of 600 C. However, somesemiconductor device fabrication processes require temperatures greaterthan 600 C.

A further embodiment of the present invention is seen in FIG. 33. As hasbeen disclosed, aluminum or aluminum alloy material, 400, may be used tojoin the shaft 404 to the plate 405 in a hermetic fashion. Further,another joining material 401 that has both the ability to bond with AlNand a higher melting temperature than aluminum, that is, greater than660 C, may be used as a structural bond to extend the usable temperatureof the shaft-plate assembly to higher temperatures. For example, atitanium-nickel alloy has been demonstrated to bond to aluminum nitrideat a temperature within the bonding temperature range used for aluminumas previously described. Other titanium and zirconium alloys may be usedas well, many of them containing silver, copper, or gold as alloyingelements. Because of their higher melting temperatures, the use of thesealloys extends the usable temperature range of the shaft-plate assemblyto 700 C or 800 C or 900 C. However, as previously discussed, theelements silver, copper, and gold may be detrimental to the crystallinestructure of wafers and must be isolated from the process environmentwith extreme care. In a similar fashion, titanium and zirconium areeasily and detrimentally oxidized when exposed to air at temperaturestypically used in wafer process. A solution is to use aluminum “guardbands” around the structural joining material, one band disposed to theprocess side if necessary to prevent the migration of detrimentalelements to the wafer, and one band disposed to the atmosphere side toprevent oxidation of the titanium or zirconium structural bond. In someembodiments, there may be a guard band on only the inner or only theouter side of the joint of other material. In some embodiments, theconcentric joints may be at different elevations, in that the end of theshaft has a plurality of plateaus wherein the joints are placed.

As seen in FIG. 33, a flange 403 is hermetically sealed, usually with anelastomeric O-ring, to the process chamber base (not shown). Electricalconnections for heating, or electrostatic chucking, or RF conduction, ortemperature monitoring, are routed through the shaft center 407 andconnect to the plate in the central area 406. Typically the electricalconnections and shaft center are in an ambient (air) environment.

After the step of joining the plate to the shaft, the shaft and/or theplate may undergo further machining in the completion of the finishedpiece. The pressures required to achieve the liquid-phase sinteringnecessary for typical previous plate-shaft joining required mechanicalstrengths higher than those provided by typical finish dimensions ofheater shafts, as the components needed to withstand the high forcesassociated with the high pressures of the previous joining process.Therefore, to reduce cracking failures during the bonding process,thicker ceramic sections may have been used for the shaft than areneeded in the final configuration. Final required dimensions are thenachieved by grinding the bonded plate/shaft assembly after bonding.Although the plate and shaft assemblies of the present invention mayundergo some further machining after joining in some embodiments, inother embodiments this is not required. The elimination of the need toutilize thick shafts to withstand forces of high contact pressurejoining of shafts and plates, as was required is past methods, removesanother time consuming and costly process step from the manufacture ofplate and shaft assemblies in processes according to embodiments of thepresent invention.

Another advantage of the joining method as described herein is thatjoints made according to some embodiments of the present invention mayallow for the disassembly of components, such as the shaft and theplate, if desired, to repair or replace one of those two components. Forexample, should a plate become damaged due to arc discharge, the platemay be removed from the assembly and replaced. This will allow the costsavings associated with the re-use of a shaft, for example. Also, withan inventory of shafts and plates on hand, a replacement heater may beassembled without need for a high temperature, high pressure process, asthe replacement component and the previously used component may bejoined according to embodiments of the present invention. Similarly,should the joint, which is both structural and hermetic, lose itshermeticity, the joint may be repaired.

A repair procedure for the unjoining of an assembly which has beenjoined according to embodiments of the present invention may proceed asfollows. The assembly may be placed in a process oven using a fixtureadapted to provide a tensile force across the joint. The fixturing mayput a tensile stress of approximately 2-30 psi onto the joint contactarea. The fixturing may put a larger stress across the joint in someembodiments. The fixtured assembly may then be placed in a process oven.The oven may be evacuated, although it may not be required during thesesteps. The temperature may be raised slowly, for example 15C per minuteto 200 C and then 20 C per minute thereafter, to standardizedtemperatures, for example 400 C, and then to a disjoining temperature.Upon reaching the disjoining temperature, the pieces may come apart fromeach other. The disjoining temperature may be specific to the materialused in the brazing layer. The disjoining temperature may be in therange of 600-800 C in some embodiments. The disjoining temperature maybe in the range of 800-1000 C in some embodiments. The fixturing may beadapted to allow for a limited amount of motion between the two piecessuch that pieces are not damaged upon separation. The disjoiningtemperature may be material specific. The disjoining temperature may bein the range of 450 C to 660 C for aluminum.

Prior to the re-use of a previously used piece, such as a ceramic shaft,the piece may be prepared for re-use by machining the joint area suchthat irregular surfaces are removed. In some embodiments, it may bedesired that all of the residual brazing material be removed such thatthe total amount of brazing material in the joint is controlled when thepiece is joined to a new mating part.

In contrast to joining methods which create diffusion layers within theceramic, joining processes according to some embodiments of the presentinvention do not result in such a diffusion layer. Thus, the ceramic andthe brazing material retain the same material properties after thebrazing step that they had prior to the brazing step. Thus, should apiece be desired to be re-used after disjoining, the same material andthe same material properties will be present in the piece, allowing forre-use with known composition and properties.

In some embodiments of the present invention, as seen in expanded viewin FIG. 34, a plate and shaft device 200 is seen with a plate assembly201 and a shaft 202. The plate assembly 201 has layers 203, 204, 205which are fully fired ceramic layers prior to their assembly into theplate assembly 201. The top plate layer 203 overlays the middle layer204 with an electrode layer 206 residing between the top plate layer 203and the middle layer 204. The middle layer 204 overlays the bottom layer205 with a heater layer 207 residing between the middle layer 204 andthe bottom layer 205.

The layers 203, 204, 205 of the plate assembly 201 may be of anon-diffusing ceramic such as aluminum nitride in the case of a heater,or other materials including alumina, doped alumina, AlN, doped AlN,beryllia, doped beryllia and others in the case of an electrostaticchuck. The layers 203, 204, 205 of the plate assembly that makes up thesubstrate support may have been fully fired ceramic prior to theirintroduction into the plate assembly 201. For example, the layers 203,204, 205 may have been fully fired as plates in a high temperature highcontact pressure specialty oven, or tape cast, or spark-plasma sintered,or other method, and then machined to final dimension as required bytheir use and their position in the stack of the plate assembly. Theplate layers 203, 204, 205 may then be joined together using a brazingprocess with joining layers 208 which allow the final assembly of theplate assembly 201 to be done without the need for a specialty hightemperature oven equipped with a press for high contact stresses.

In embodiments wherein a shaft is also part of the final assembly, suchas in the case of a plate and shaft device, the plate assembly 201 toshaft 202 joining process step may also use a brazing process donewithout the need for a specialty high temperature oven equipped with apress for high contact stresses. The joining of the plate layers, andthe plate assembly to the shaft, may be done in a simultaneous processstep in some embodiments. The shaft 202 may be joined to the plateassembly 201 with a joining layer 209. The joining layer 209 may be abrazing element which is identical to the joining layers 208 in someembodiments.

An improved method for manufacturing a plate, or plate assembly, mayinvolve the joining of layers of the plate assembly, which have beendescribed above and are described in more detail below, into a finalplate assembly without the time consuming and expensive step of anadditional processing with high temperatures and high contact pressures.The plate layers may be joined with a brazing method for joiningceramics according to embodiments of the present invention. An exampleof a brazing method for joining together first and second ceramicobjects may include the steps of bringing the first and second objectstogether with a brazing layer selected from the group consisting ofaluminum and an aluminum alloy disposed between the first and secondceramic objects, heating the brazing layer to a temperature of at least800 C, and cooling the brazing layer to a temperature below its meltingpoint so that the brazing layer hardens and creates a hermetic seal soas to join the first member to the second member. In some aspects, thebrazing temperature is at least 770 C. In some aspects, the brazingtemperature is in the range of 770 C to 1200 C. Various geometries ofbraze joints may be implemented according to methods described herein.

In some embodiments of the present invention a plate assembly withlayers may be presented such that standoffs are present between thelayers of the plate such that when the joining layer is heated, andslight pressure is applied axially to the plates, there is slight axialcompression such that the joining layer is mildly thinned until thestandoff on one plate contacts the adjacent plate. In some aspects, thisallows for not just control of the joint thickness but also fordimensional and tolerance control of the plate assembly. For example,the parallelism of features of the various plates can be set by machinetolerances on the plate layers, and this aspect can be maintained duringthe joining process with the use of standoffs. In some embodiments,post-joining dimensional control may be achieved using a circumferentialouter ring on one plate layer which overlays an inner ring on anadjacent layer to provide axial conformance. In some embodiments, one ofthe outer ring or the inner ring may also contact the adjacent plate inan axial direction perpendicular to the plate such that positionalcontrol is also achieved in that axial direction. The axial positionalcontrol may also thus determine the final thickness of a joining layerbetween the two adjacent plates.

In some embodiments of the present invention an electrode between layersmay be of the same material as the joining layer, and may function in adual capacity of both the joining layer and the electrode. For example,the area previously occupied by an electrode in an electrostatic chuckmay instead be occupied by a joining layer which has the dual functionof performing as an electrode, for providing electrostatic clampingforce for example, and of performing as a joining layer to join the twoplates between which the joining layer resides. In such embodiments, alabyrinth may be around the periphery of the two joined plate such thatline of sight, and access in general, to the charged electrode from aregion outside of the plate is minimized.

FIG. 35 illustrates a partial cross-section of a plate assembly 240according to some embodiments of the present invention. The plateassembly 240 may be adapted to be joined to a shaft to complete a plateand shaft assembly. The top plate layer 241 may be a circular discadapted to support a substrate during semiconductor processing steps. Aheater 244 is adapted to reside below the top plate layer 241. Theheater may be attached or adhered to one or both of the plate layers.The top plate layer 241 overlays the bottom plate layer 242. A joininglayer 243 joins the top plate layer 241 to the bottom plate 242. Thejoining layer may be an annular disc. In some embodiments, the top platelayer and the bottom plate layer are ceramic. In some embodiments, thetop plate layer and the bottom plate layer are aluminum nitride. The topplate layer and the bottom plate layer may be a non-diffusing ceramicfrom the group which includes aluminum nitride, alumina, zirconia, andberyllium oxide. In some embodiments the joining layer is aluminum.Examples of the joining process and materials are discussed below.

FIG. 36 illustrates a partial cross-section of a plate assembly 260according to some embodiments of the present invention. The plateassembly 260 is a multi-layer plate assembly with both a heater and anelectrode residing between different layers. The layers are joined withbrazing elements and the final position of the plates in a directionperpendicular to the plane of the primary plane of the plates isdictated by standoffs 268 on the plates.

A top plate layer 261 overlays a lower plate layer 262. The lower platelayer 262 overlays a bottom plate layer 263. Although illustrated inFIG. 36 with three plate layers, different numbers of plate layers maybe used according to the needs of a particular application. The topplate layer 261 is joined to the lower plate layer 262 using amulti-function joining layer 266. The multi-function joining layer 266is adapted to provide joining of the top plate layer 261 to the lowerplate layer 262 and to be an electrode. FIG. 41 illustrates anembodiment of such an electrode. Such an electrode may be a joininglayer that is substantially a circular disc, wherein the joiningmaterial also functions as an electrode. As seen in FIG. 36, a standoff268 is adapted to provide positional control of the top plate layer 261to the lower plate layer 262 in a vertical direction perpendicular tothe primary plane of the plate layers. The rim of the top plate layer261 is adapted to remove line of sight along the boundary 267 betweenthe two plates at their periphery. The thickness of the joining layer266 may be sized such that the joining layer 266 is in contact with thetop plate layer 261 and the lower plate layer 262 prior to the step ofheating and joining the plate assembly.

The lower plate layer 262 overlays the bottom plate layer 263. A heater264 resides between the lower plate layer 262 and the bottom plate layer263. A joining layer 265 joins the lower plate layer 262 to the bottomplate layer 263. The joining layer 265 may be an annular ring within theperiphery of the plate layers. A standoff 269 is adapted to providepositional control of the lower plate layer 262 to the bottom platelayer 263 in a vertical direction perpendicular to the primary plane ofthe plate layers. During a joining step of the plate assembly, thecomponents as seen in FIG. 36 may be pre-assembled, and then this platepre-assembly may be joined using processes described herein to form acompleted plate assembly. In some embodiments, this plate pre-assemblymay be further preassembled with a shaft and shaft joining layer suchthat a complete plate and shaft device may be joined in a single heatingprocess. This single heating process may not require a high temperatureoven, or a high temperature oven with presses adapted to provide highcontact stresses. In addition, in some embodiments the completed plateand shaft assembly may not require any post-joining machining yet maystill meet the tolerance requirements of such a device in actual use insemiconductor manufacturing.

FIG. 37 illustrates a partial cross-sectional view of two plate layers220, 221 wherein a reservoir 226 is seen in the bottom plate layer 221.A top plate layer 220 may overlay a bottom plate layer 221. An electrodeportion 223 may be present in between the top plate layer 220 and thebottom plate layer 221. A standoff 225 is adapted to provide positionalcontrol of the top plate layer 220 to the bottom plate layer 263 in avertical direction perpendicular to the primary plane of the platelayers. A reservoir 226 may reside in the bottom plate layer radiallyoutside of the joining layer 222. The reservoir 226 is positioned suchthat possible excess joining material from the joining layer may becaptured in the reservoir, and not move into the labyrinth 224. In thecase of a plate wherein the electrode and the joining layer are the samefeature, as seen in the electrode 266 of FIG. 6, the reservoir may bemore important as the joining layer, and its possible excess, may beelectrically charged and thus not appropriate to seep towards outerperiphery of the plate assembly.

In some embodiments, a plate layer may include channels adapted for therouting of gasses through the substrate assembly. A plate layer may havechannels, wherein the material of the plate layer between the channelsis joined to the adjacent plate according to methods of the presentinvention. Thus, an individual plate layer could be manufactured suchthat the channels are present in the final fully fired ceramic piece,and this piece may be joined to the adjacent layer. The channels may becoupled to the shaft and/or conduits within the shaft in someembodiments.

One embodiment of a brazing method for joining together plate layers,which may be made of aluminum nitride, to form the plate assembly, maybe implemented as follows. A sheet of aluminum or aluminum alloy metalbinder or filler may be provided between the plate layers, and also theshaft and the bottom plate layer in some aspects, and the plate layersmay be brought together with the sheet of the metal binder disposedtherebetween. The metal binder or filler may then be heated in a vacuumto a temperature of at least 800 C and cooled to a temperature below 600C so that the metal binder or filler hardens and creates a hermetic sealjoining the plate layers to each other into a plate assembly, andjoining the shaft to the plate assembly. In some aspects, the brazelayer may be heated in a vacuum to a temperature of at least 770 C. Insome aspects, the braze layer may be heated to a temperature in therange of 770 C to 1200 C.

In an exemplary embodiment, the plate layers may be of aluminum nitrideand have been separately formed previously using a liquid phasesintering process. The plate layers may be approximately 200 mm to 300mm in diameter and 0.1 to 0.75 inches thick in some embodiments. Theshaft may be a hollow cylinder which is 5-10 inches long with a wallthickness of 0.1 inches. The bottom of the plate assembly may have arecess adapted to receive an outer surface of a first end of the shaft.The plate assembly and shaft may be fixtured together for a joining stepwith a brazing material of aluminum foil placed between the pieces atthe appropriate pre-determined joining locations. The fixturing may puta contact pressure of approximately 2-200 psi onto the joint contactareas. In some embodiments the contact pressure may be in the range of2-40 psi. The contact pressure used at this step is significantly lowerthan that seen in the joining step using hot pressing/sintering as seenin prior processes, which may use pressures in the range of 2000-3000psi. With the much lower contact pressures of the present methods, thespecialized presses of the previous methods are not needed. Thepressures needed for the joining of the plate layers to each other intoa plate assembly, and of the plate assembly to the shaft using thepresent methods may be able to be provided using simple fixturing, whichmay include a mass placed onto the fixturing using gravity to providethe contact pressure. In some embodiments, contact between the interfaceportions of the plate layers, and of the shaft and the brazing element,as well as contact between the interface portion of the plates and thebrazing element, will provide contact pressure sufficient for joining.Thus, the fixture assembly need not be acted upon by a press separatefrom the fixture assembly itself. The fixtured assembly may then beplaced in a process oven. The oven may be evacuated to a pressure of1×10E−5 Torr. In some aspects, vacuum is applied to remove residualoxygen. In some embodiments, a vacuum of more than 1×10E−4 Torr is used.In some embodiments, a vacuum of more than 1×10E−5 Torr is used. Of notewith regard to this step is that the high temperature oven with highcontact pressure fixturing, which was required during the manufacture ofthe ceramic components (shaft and plate), is not needed for this joiningstep. Upon initiating the heating cycle, the temperature may be raisedslowly, for example 15C per minute to 200 C and then 20 C per minutethereafter, to standardized temperatures, for example, 600 C and thejoining temperature, and held at each temperature for a fixed dwell timeto allow the vacuum to recover after heating, in order to minimizegradients and/or for other reasons. When the braze temperature has beenreached, the temperature can be held for a time to effect the brazereaction. In an exemplary embodiment, the dwell temperature may be 800 Cand the dwell time may be 2 hours. In another exemplary embodiment, thedwell temperature may be 1100 C and the dwell time may be 15 minutes. Inanother exemplary embodiment, the dwell temperature may be 1075 C andthe dwell time may be 1 hours. In some embodiments, the dwelltemperature does not exceed a maximum of 1100 C. In some embodiments,the dwell temperature does not exceed a maximum of 1300 C. In someembodiments, the dwell temperature does not exceed a maximum of 1400 C.Upon achieving sufficient braze dwell time, the furnace may be cooled ata rate of 20 C per minute, or lower when the inherent furnace coolingrate is less, to room temperature. The furnace may be brought toatmospheric pressure, opened and the brazed assembly may be removed forinspection, characterization and/or evaluation.

FIGS. 38-40 illustrates embodiments of heater elements between platelayers in a substrate support assembly according to some embodiments ofthe present invention.

In some embodiments, the plate may be circular. In some embodiments, theplate may be square. In some embodiments, the plate may be a differentshape.

In some embodiments of a multi-layer plate device, for example a devicewithout a shaft, layers of ceramic may overlay a base of metal, or othermaterial. In such embodiments, joining of the layers to each other, andto the base, may be performed using processes as described herein. Insome embodiments, layers of other material may be interspersed betweenother ceramic layers.

As evident from the above description, a wide variety of embodiments maybe configured from the description given herein and additionaladvantages and modifications will readily occur to those skilled in theart. The invention in its broader aspects is, therefore, not limited tothe specific details and illustrative examples shown and described.Accordingly, departures from such details may be made without departingfrom the spirit or scope of the applicant's general invention.

What is claimed is:
 1. A method for the manufacture of a ceramicmulti-layer plate device used as a plate in an electrostatic chuck, orin a heater, or other wafer support, used in semiconductor waferprocessing, said method comprising the steps of: depositing aluminumonto one or both of a joining interface surface of an upper plate layerand a joining interface surface of a lower plate layer, wherein saidjoining interface surfaces of said upper plate layer and said lowerplate layer are annular rings around an outer area of said upper platelayer and said lower plate area; arranging said upper plate layer andsaid lower plate layer into a stack to form a joining pre-assembly,wherein said aluminum is disposed between said upper plate layer andsaid lower plate layer, thereby defining an inner space between saidupper plate layer and said lower plate layer within the interior of thedeposited aluminum, wherein said upper plate layer comprises a ceramicfrom the group of aluminum nitride, alumina, beryllium oxide, andzirconia, and said lower plate layer comprises a ceramic from the groupof aluminum nitride, alumina, beryllium oxide, and zirconia, and whereinsaid aluminum comprises 99% by weight or greater aluminum; placing thecomponents of said joining pre-assembly into a process chamber; removingoxygen from said process chamber; heating at least said aluminum brazingelement of said joining pre-assembly to a first joining temperature ofbetween 770 C and 1200 C, thereby joining said upper plate layer to saidlower plate layer with a hermetically sealed aluminum joint whichhermetically seals said inner space from an area outside of said brazinglayer across said joint, and wherein said aluminum has not diffused intosaid upper plate layer or said lower plate layer, and wherein thethickness of said final joint is greater than zero.
 2. The method ofclaim 1 wherein the step of removing oxygen from said process chambercomprises applying a pressure of lower than 1×10E−4 Torr to said processchamber.
 3. The method of claim 1 wherein the step of removing oxygenfrom said process chamber comprises applying a pressure of lower than1×10E−5 Torr to said process chamber.
 4. The method of claim 1 whereinthe step of removing oxygen from said process chamber comprises purgingand re-filling the chamber with pure, dehydrated inert gas.
 5. Themethod of claim 1 wherein the step of removing oxygen from said processchamber comprises purging and re-filling the chamber with purifiedhydrogen.
 6. The method of claim 1 wherein said step of heating saidjoining pre-assembly to a first joining temperature comprises heatingsaid joining pre-assembly for a duration of between 10 minutes and 2hours.
 7. The method of claim 1 wherein said step of heating saidjoining pre-assembly to a first joining temperature comprises heatingsaid joining pre-assembly for a duration of between 30 minutes and 1hour.